Oil and gas wells are completed in many different ways and have a variety of different designs. Some wells have cemented inner casings and some wells have uncemented inner casings. Cemented casings are completed after cementing the intermediate casing A and the lower part of the well is drilled so that the inner casing B can be submerged into the well, as shown in FIG. 1A. The cement is then led down the inner casing and out into the annulus C. In the event that, after the borehole has been drilled, tests show that the hydrostatic pressure in the annulus is too high for the cement to rise sufficiently in the annulus, the upper part of the inner casing is removed and replaced by a drill pipe, as shown in FIG. 1B. When replacing the upper part of the inner casing with a drill pipe, the annular space D between the intermediate casing and the inner casing is increased, thereby decreasing the hydrostatic pressure, which allows for the cement to be pressured up to the predetermined level shown in FIG. 1B.
In order to be able to replace the upper inner casing with a drill pipe, the inner casing has a receptacle R into which sealing elements of the upper inner casing can be fit to create a good sealed connection after the drill pipe has been retracted. However, these sealed connections tend to deteriorate over time even though they have never been used, and thus, such wells may leak over time.